使用php WordPress提交表单

Hello I work with WordPress , and I create a custom Modal with form to add a Group called 'abonnement' I added the table in Database and this is my issue:

Form

<form name="abonnementCreate" action="create.php" method="POST">
  <div class="form-group">
    <label>Nom de l'abonnemnt</label>
    <input type="text" class="form-control" id="nomA" name="nomA">
  </div>
  <div class="form-group">
    <label>Durée</label>
    <input type="number" class="form-control" id="dureeA">
    <small id="dureeHelp" class="form-text text-muted">En jours</small>
  </div>
  <div class="form-group">
    <label>Nombre de produit autorisé</label>
    <input type="number" class="form-control" id="nbProdA">
  </div>
  <div class="form-group">
    <label>Frais d'abonnement (€)</label>
    <input type="number" class="form-control" id="fraisA">
  </div>
  <button type="submit" name="create" class="btn btn-primary">Valider</button>
</form>

and this is the action of the creation :

create.php

<?php
  include'admin.php';
  global $wpdb;

  if(isset( $_POST["create"]))
   {
     $wpdb->insert('abonnement', array(
     'nom' => '.$_POST["nomA"].',
     'duree' => '.$_POST["dureeA"].',
     'nbProd' => '.$_POST["nbProdA"].',
     'frais' => '.$_POST["fraisA"].' 
      ));
    }
 ?>

I have $_POST["create"] and the condition is true but $_POST[" any field"] is always null,
Someone please can help me ?

you can never catch the post value from id of the form input field.only way that you can get value using $_POST[] is using the "name" attribute of the input field.

    <input type="text" class="form-control" id="nomA" name="name1">

this input field value can be accessed from form action php file using $_POST["name1"]